Ultrasound transducers are widely used in many different fields, including ultrasound imaging. In many conventional medical imaging applications, ultrasound transducers are constructed from piezoelectric materials, such as lead zirconate titanate (PZT). Another type of ultrasound transducer that has been developed for various applications including ultrasound imaging is the capacitive micromachined ultrasonic transducer (CMUT). Similar to a PZT transducer, a CMUT transducer may be activated by electrical pulses to generate acoustic signals that propagate in tissues; however, unlike a PZT transducer, a CMUT transducer may employ an additional bias voltage, such as when transmitting and/or receiving ultrasound signals. Traditionally, the bias voltage may be a DC voltage that remains constant during imaging operations.
Furthermore, CMUTs may be arranged in arrays. For example, a 1D transducer array may include multiple CMUT elements arranged in only one dimension, e.g., the azimuth dimension. This arrangement of elements allows the formation of focused beams for improved imaging resolution. In addition, for beams formed by the received signals, the focal depth may be shifted dynamically during imaging for a more uniform resolution. In another dimension, i.e., the elevation dimension, however, the focus of a 1D transducer array is fixed. Because of the fixed focal length, the elevation slice thickness may not be uniform with depth and the imaging performance of the 1D transducer array may be compromised.
One solution to this problem is to use a 1.5D transducer array. For example, a 1.5D transducer array may include at least two rows of elements separated in the elevation dimension. The spacing between the two adjacent rows may be much larger than the wavelength. Further, the number of rows may increase with penetration depth for optimal imaging performance from near field to far field. Further, the number of elements of 1.5D arrays is usually significantly larger than the number of channels of the respective imaging systems. Therefore, high voltage analog switches may be used for selecting desired elements in 1.5D arrays for transmission and/or reception.